1. Field of the Invention
The invention relates to the field of siphonic, gravity-powered toilets for the removal of human and other waste, and more specifically to a toilet having a dual flushing system.
2. Description of Related Art
Toilets for removing waste products, such as human waste, are well known. Gravity-powered toilets generally have two main parts: a tank and a bowl. The tank and bowl can be separate pieces, which are coupled together to form the toilet system (commonly referred to as a two-piece toilet), or can be combined into one integral unit (typically referred to as a one-piece toilet).
The tank, which is usually positioned over the back of the bowl, contains water that is used for initiating flushing of waste from the bowl into a sewage line, as well as for refilling of the bowl with fresh water. When a user desires to flush the toilet, he initiates a flushing mechanism, by pushing down on a flush lever on the outside of the tank, which is connected on the inside of the tank to a movable chain or lever. When the flush lever is depressed, it moves a chain or lever on the inside of the tank, which acts to lift and open a flush valve, causing water to flow from the tank into the bowl, thus initiating the toilet flush.
There are three general purposes to be served in a flush cycle. The first is removal of solid or other waste to a drain line. The second is cleansing of the bowl to remove any solid or liquid waste deposited or adhered to the surfaces of the bowl. The third is replenishing the pre-flush water volume in the bowl so that relatively clean water remains in the bowl between uses and that a sufficient seal is formed to prevent sewer gases from flowing into the room. The second requirement, cleansing the bowl, is usually achieved by way of a rim that extends around an upper perimeter of the toilet bowl that defines a rim channel running through the rim around the perimeter. Some or all of the flush water is directed through this rim channel and flows through openings positioned in the rim providing liquid communication between the channel and the bowl so as to disperse water over the entire surface of the bowl and accomplish the required cleansing.
Gravity-powered toilets fall generally into two categories: wash down and siphonic. In a wash-down toilet, the water level within the bowl of the toilet remains relatively constant at all times. When a flush cycle is initiated, water flows from the tank and spills into the bowl. This causes a rapid rise in water level and the excess water spills over the weir of the trapway, carrying liquid and solid waste along with it. At the conclusion of the flush cycle, the water level in the bowl naturally returns to the equilibrium level determined by the height of the weir.
In a siphonic toilet, the trapway and other hydraulic channels are designed such that a siphon is initiated in the trapway upon addition of water to the bowl. The siphon tube itself is an upside down curved, generally U-shaped tube that draws water from the toilet bowl to the wastewater line. When the flush cycle is initiated, water flows into the bowl and spills over the weir in the trapway faster than it can exit the outlet to the sewer line. Sufficient air is eventually removed from the down leg of the trapway to initiate a siphon, which in turn pulls the remaining water by vacuum out of the bowl. The water level in the bowl when the siphon breaks is consequently well below the level of the weir, and a separate mechanism needs to be provided to refill the bowl of the toilet at the end of a siphonic flush cycle to reestablish the original water level and protective “seal” against back flow of sewer gas.
Siphonic and wash-down toilets each have inherent advantages and disadvantages. Wash-down toilets can function with larger trapways than siphonic toilets, but generally require a smaller amount of pre-flush water in the bowl to achieve the 100:1 dilution level required by plumbing codes in most countries (That is, 99% of the pre-flush water volume in the bowl must be removed from the bowl and replaced with fresh water during the flush cycle). This small pre-flush volume manifests itself as a small “water spot.” The water spot, or surface area of the pre-flush water in the bowl, plays an important role in maintaining the cleanliness of a toilet and reducing odors. A large water spot increases the probability that waste matter will contact water before contacting the ceramic surface of the toilet. This reduces adhesion of waste matter to the ceramic surface making it easier for the toilet to clean itself via the flush cycle. Wash-down toilets with their small water spots therefore frequently require manual cleaning of the bowl after use. The adhesion of waste material above the water line also leads to a greater level of unpleasant smell during use.
Siphonic toilets, due to the requirement that most of the air be removed from the down leg of the trapway in order to initiate a siphon, tend to have smaller trapways which can result in clogging. Siphonic toilets have the advantage of being able to function with a greater pre-flush water volume in the bowl and greater water spot. This is possible because the siphon action pulls the majority of the pre-flush water volume from the bowl at the end of the flush cycle. As the tank refills, a portion of the refill water is directed into the bowl to return the pre-flush water volume to its original level. In this manner, the 100:1 dilution level required by many plumbing codes is achieved even though the starting volume of water in the bowl is significantly higher relative to the flush water exited from the tank. In the North American markets, siphonic toilets have gained widespread acceptance and are now viewed as the standard, accepted form of toilet. In European markets, wash-down toilets are still more accepted and popular. Whereas both versions are common in the Asian markets.
Gravity-powered siphonic toilets generally fall into three categories, depending on the design of the hydraulic channels used to achieve the flushing action. These categories are: non-jetted, rim jetted, and direct jetted.
In non-jetted bowls, all of the flush water exits the tank and enters the bowl through a “tank inlet area” in the bowl and flows through a manifold into the rim channel. The water is dispersed around the perimeter of the bowl via a series of holes positioned underneath the rim. Some of the holes are designed to be larger in size to allow greater flow of water into the bowl. A relatively high flow rate is needed to spill water over the weir of the trapway rapidly enough to displace sufficient air in the down leg and initiate the siphon. Non-jetted bowls typically have adequate to good performance with respect to cleansing of the bowl and replenishment of the pre-flush water, but are relatively poor in performance in terms of bulk removal. The feed of water to the trapway is inefficient and turbulent, which makes it more difficult to sufficiently fill the down leg of the trapway and initiate a strong siphon. Consequently, the trapway of a non-jetted toilet is typically smaller in diameter and contains bends and constrictions designed to impede flow of water. Without the smaller size, bends, and constrictions, a strong siphon would not be achieved. Unfortunately, the smaller size, bends, and constrictions result in poor performance in terms of bulk waste removal and frequent clogging, conditions that are extremely dissatisfying to end users.
Designers and engineers of toilets have improved the bulk waste removal of siphonic toilets by incorporating “jets.” In a rim-jetted toilet bowl, the flush water exits the tank through the tank inlet area and flows through a manifold into the rim channel. A portion of the water is dispersed around the perimeter of the bowl via a series of holes positioned underneath the rim. The remaining portion of water flows through a jet channel positioned at the front of the rim. This jet channel connects the rim channel to a jet opening positioned in the sump of the bowl. The jet opening is sized and positioned to send a powerful stream of water directly at the opening of the trapway. When water flows through the jet opening, it serves to fill the trapway more efficiently and rapidly than can be achieved in a non-jetted bowl. This more energetic and rapid flow of water to the trapway enables toilets to be designed with larger trapway diameters and fewer bends and constrictions, which, in turn, improves the performance in bulk waste removal relative to non-jetted bowls. Although a smaller volume of water flows out of the rim of a rim-jetted toilet, the bowl cleansing function is generally acceptable as the water that flows through the rim channel is pressurized. This allows the water to exit the rim holes with higher energy and do a more effective job of cleansing the bowl.
Although rim-jetted bowls are generally superior to non-jetted, the long pathway that the water must travel through the rim to the jet opening dissipates and wastes much of the available energy. Direct-jetted bowls improve on this concept and can deliver even greater performance in terms of bulk removal of waste. In a direct-jetted bowl, the flush water exits the tank through the tank inlet area in the bowl and flows through a manifold. At this point, the water is divided into two portions: a portion that flows through the rim channel with the primary purpose of achieving the desired bowl cleansing, and a portion that flows through a second “direct jet channel” that connects the manifold to a jet opening in the sump of the toilet bowl. The direct jet channel can take different forms, sometimes being unidirectional around one side of the toilet, or being “dual fed,” wherein symmetrical channels travel down both sides connecting the manifold to the jet opening. As with the rim-jetted bowls, the jet opening is sized and positioned to send a powerful stream of water directly at the opening of the trapway. When water flows through the jet opening, it serves to fill the trapway more efficiently and rapidly than can be achieved in a non-jetted or rim jetted bowl. This more energetic and rapid flow of water to the trapway enables toilets to be designed with even larger trapway diameters and minimal bends and constrictions, which, in turn, improves the performance in bulk waste removal relative to non-jetted and rim jetted bowls.
Several inventions have been aimed at improving the performance of siphonic toilets through optimization of the direct-jetted concept. For example, U.S. Pat. No. 5,918,325 suggests improving performance of a siphonic toilet by improving the shape of the trapway. U.S. Pat. No. 6,715,162 suggests improving performance by the use of a flush valve with a radius incorporated into the inlet and asymmetrical flow of the water into the bowl.
However, given the increasing demands for environmental water conservation, there is still a need for improvement. Government agencies have continually demanded that municipal water users reduce the amount of water they use. Much of the focus in recent years has been to reduce the water demand required by toilet flushing operations. In order to illustrate this point, the amount of water used in a toilet for each flush has gradually been reduced by governmental agencies from 7 gallons/flush (prior to the 1950's), to 5.5 gallons/flush (by the end of the 1960's), to 3.5 gallons/flush (in the 1980's). The National Energy Policy Act of 1995 now mandates that toilets sold in the United States use water in an amount of only 1.6 gallons/flush (6 liters/flush). Regulations have recently been passed in the State of California that require water usage to be lowered ever further to 1.28 gallons/flush. The 1.6 gallons/flush toilets currently described in the patent literature and available commercially lose the ability to consistently siphon when pushed to these lower levels of water consumption.
Thus, there is significant need in the art for a toilet system that enables lower water usage without sacrificing performance in terms of bulk removal and cleanliness of the bowl.
One potential route to fulfilling the above-noted need in the art is through the use of toilet systems that are capable of operating at multiple flush volumes. For example, “dual flush” toilets are now commercially available that offer two flush cycles. The user of the toilet can select a “full flush” of, for example, 1.6 gallons for removal of solid waste or a “short flush” of, for example, 1.1 gallons for the removal of liquid or minimal solid waste. Assuming that toilets are used roughly twice as often for removal of liquid waste than removal of solid waste, this representative dual flush system results in an average water usage, Vavg, of(2Vpf+Vff)/3  (I)wherein Vpf is the volume of a partial (or lower volume) flush and Vff is the volume of the full flush. In the example above regarding typical flush volumes wherein gpf is gallons/flush,Vavg=(2·1.1 gpf+1.6 gpf)/3=1.27 gpf  (II)This corresponds to a 21% savings over a single-flush, 1.6 gallons per flush system.
Recently, the U.S. Environmental Protection Agency introduced a WaterSense program that certifies toilets that use less than or equal to 1.28 gpf (20% or greater savings over 1.6 gpf) as “High Efficiency Toilets,” or HETs. Regional programs that offer rebates for purchasing WaterSense certified HETs are growing in popularity and will drive consumers towards the purchase of these products.
However, the dual flush toilets currently available in the world market are lacking in some dimension of toilet performance. In fact, truly siphonic dual flush toilets do not exist. Dual flush toilets are commercially available but function primarily as wash-down systems and suffer problems associated with maintenance of bowl cleanliness as discussed above. In the U.S. market, where siphonic toilets are the norm, consumer reluctance to accept wash-down dual flush toilets will slow the efforts of the U.S. government to reduce water usage through the WaterSense program.
The technical challenge in designing truly siphonic dual flush toilets has been two-fold: The first is designing a toilet capable of siphoning consistently on very low (<1.28 gpf) flush volumes. The second is in finding a way to consistently refill the bowl after varying flush cycles. As mentioned above, the level of water in the bowl of a gravity-powered siphonic toilet system falls below the level of the weir after the break of the siphon. The water level must be restored to its original level or at minimum to the 2 inch (5.08 cm) seal depth required by plumbing codes throughout North America, Europe, and Asia. This refilling is accomplished by directing into the bowl a predetermined percentage of the water required to refill the tank. This predetermined percentage is referred to as the “refill ratio.” The system and refill ratio are tuned such that the level of water in the bowl reaches its required seal depth at nearly the same time that the water level in the tank reaches its required depth and the fill valve is closed. The closing of the fill valve is usually controlled by means of a float inside the tank. When the tank water level reaches its target height, the float rises on the surface of the water and mechanically closes the fill valve.
With a dual flush toilet system, a different volume of water will flow from the tank depending on the flush cycle the user selects. For example, when the full cycle (6 liters per flush (lpf)) is selected, approximately 4.5 liters of water will flow from the tank and 1.5 liters of the water originally in the bowl will be siphoned down the drain along with it. The refill ratio must therefore be set to direct 1.5 liters of water back into the bowl during the time it takes to return 4.5 liters to the tank. The refill ratio in this example is then 1.5 liters/6.0 liters=25%. Setting the refill ratio at 25% will result in maintenance of seal depth and proper function of the toilet system when the full flush cycle is activated. To further the example, when the short flush is selected, approximately 3.3 liters of water will flow from the tank and 1.5 liters of the water originally in the bowl will be siphoned down the drain along with it. After the flush, the tank only needs to replenish 3.3 liters of water. If the same 25% refill ratio is used, only 1.1 liters will be returned to the bowl, leaving it short of its code required seal depth. The solution to this problem is not obvious, and toilet manufacturers have been forced to turn to wash-down systems that circumvent the issue by eliminating the need for refill.
There is therefore, a need in the art for a siphonic toilet system that provides high-performance waste removal, while solving the refill issue and minimizing clogging, and still allowing for conservation of water use.